Phosphotungstic acid loaded on hydrophilic ionic liquid modified SBA-15 for selective oxidation of alcohols with aqueous H2O2

Phosphotungstic acid (H3PW12O40) has been successfully loaded onto amino-functionalized ionic liquid modified mesoporous silica SBA-15 by totally anion-exchange and partly protonating in the channel of SBA-15 with Keggin-type H3PW12O40. XRD patterns, N2 adsorption–desorption isotherms and TEM images confirm the intact mesostructures of the samples. Thermal analysis, 29Si MAS NMR and 31P MAS NMR indicate the presence of the [PW12O40]3− (PW) in the mesopores. FT-IR spectra suggest that a portion of free amino groups in the amino-functionalized IL moiety are remained in the channel of the catalysts, although there are ionic interactions between PW anions and protonated amino groups, as well as between PW anions and imidazolium cations. Hydrophilic amino-functionalized IL moiety in the mesostructures, especially, the remained free amino groups flexibly anchored on the imidazolium, plays a crucial role in enhancing the accessibility of H2O2, which in turns significantly improves the catalytic performance. The resultant PW loaded on amino-functionalized IL modified SBA-15 (PW-NH2-IL-SBA-15) catalysts are proven to be versatile in the solvent-free oxidation of alcohols with aqueous 30% H2O2, presenting high efficiency, convenient recovery and steady reuse.

Phosphotungstic acid loaded onto the amino-functionalized ionic liquid modified SBA-15 have proved to be the effective, versatile and reusable heterogeneous catalysts for the selective oxidation of alcohols with 30% H2O2.Figure optionsDownload as PowerPoint slideHighlights
► NH2-functionalized IL modified SBA-15 was first used to supported the phosphotungstate.
► The mixed cations (NH3+ and imidazolium) activated the [PW12O40]3− species.
► The hydrophilic IL and remained free amine groups enhanced the accessibility of H2O2.
► The catalyst presented high efficiency, convenient recovery and steady reuse.